Appliance Wiring Material

hi can i use a # 6 awm stranded type wire from a main panel to a sub panel in conduit under ground? it will have 40 amps or less on it. this is what it says on the wire. awm mil 6awg/133 fep 600v 200c from what i read online i think its silicon based its oily when you touch it . this might be a unusual way to use this wire but with the price of copper if will work it will save me money
thanks??